Substances similar to insulin, ACTH and somatostatin are present in unicellular organisms and higher plants. The studies were extended to further characterize the insulin-related molecule in spinach, Lemna and rye. Using gel chromatography and high performance liquid chromatography the insulin-related materials were partially purified and the activity demonstrated by specific radioimmunoassay and bioassays. To isolate the genes encoding these peptide hormones in multicellular nonvertebrates and unicellular organisms recombinant DNA technology is being used. Using lambda gtII expression vectors, Drosophilia and yeast DNA was probed for the expression of insulin and insulin-related peptides using antiinsulin antibodies. In addition rat IGF-I cDNA was cloned and sequenced to be used as an additional tool in the search for insulin-related genes in primitive eukaryotes and prokaryotes.